This invention relates to the protection of plastics, polymeric materials, and cellulosic materials against attack by microorganisms.
Synthetic, film-forming materials such as those used in the manufacture of plastic or polymeric films, and various types of plastics or polymers, are known to be subject to attack by microorganisms. Such microorganisms include bacteria, fungi and actinomycetes. The last mentioned are microorganisms found in soil which contain no chlorophyll. They are usually classified with the bacteria, but resemble both bacteria and fungi; they are intermediate in size between fungi and bacteria.
Such microorganisms attack plastics and polymers and can cause damage or deterioration ranging from discoloration and staining to embrittlement or actual disintegration, depending on the type of plastic or polymer, and the environment in which it is situated. Severe damage can be produced to plastics or polymers which are utilized in certain environments, such as those with high humidity. Plastics and polymers are commonly used for instance, in underground construction, in pipes and conduits, cables, sheathing, insulation, etc. In such an environment, they are subject to severe deterioration by soil-borne microorganisms. Similarly, plastics and polymers used in materials such as swimming pool liners, awnings, camping equipment, and other articles for outdoor use, and in upholstery, car tops, shoes, boots and clothing, in which they may be exposed to natural humidity and/or sweat, possibly in combination with somewhat elevated temperatures, and subject to microbial deterioration.
In addition to physical deterioration of plastics and polymers, microorganisms growing on the surface of such materials can cause discoloration and/or staining thereof resulting in a shortening of the useful life of said materials for at least aesthetic purposes. Actinomycetes, in particular, growing on the surfaces of plastics and polymers can produce colored byproduct dyes which are soluble in the plasticizers used in such substances, and which migrate through the substance via the plasticizer, resulting in the phenomenon known as "pink staining." In addition, surface growth of microorganisms on polymers may interfere with functional performance, for instance when used as lubricating surfaces.
In order to prevent attack and deterioration or discoloration of polymeric or plastic materials by microorganisms, a number of compounds have been used as industrial biocides.
For use as a biocide in connection with plastics and polymers, a compound must have the following properties:
effectiveness at low levels against many microorganisms;
compatibility with plasticizers and other chemicals used in the formulation of plastic and polymeric products;
lack of a disadvantageous color or odor;
resistance to leaching from plastic or polymeric materials;
and particularly;
(a) thermal stability at temperatures over 300.degree. F. (148.degree. C.) so that deterioration of the biocide does not occur during the processing of plastics and polymers;
(b) mobility--the ability to migrate through the plastic, polymer or plasticizer utilized therein, so as to be dissipated therethrough; and
(c) stability towards ultraviolet and other light radiation.
Such properties are necessary for plastics and polymers which are cast, rolled, molded, extruded, or otherwise fabricated into a continuous form, for use in various ways such as raw materials for the manufacture of plastic or polymer articles or as plastic or polymeric coatings, as well as plastics and polymers which are knitted or woven into continuous fibers.
Similarly, cellulosic materials, such as cotton and other fibers are subject to damage or deterioration by microorganisms; industrial biocides have been used to protect such materials, and articles formed from them, from microbial deterioration. Properties such as stability toward ultraviolet light and heat are also required of biocides for such materials.
Both the prevention of growth in the contact area, that is on the material itself, and inhibition of growth in a zone surrounding the contact area, are of importance in order to prevent the spread of an actively growing organism. The biocide must possess a positive antimicrobial activity in a zone of inhibition surrounding the article; otherwise, a compound which is effective as a biocide in the contact area itself would nevertheless not control heavy growth on the surface or on substances associated with or attached to the material. Such property is important, for instance, for fabrics in which a polymeric fiber, such as a polyester or polyamide, is laminated to a cotton or other cellulosic backing such as canvas.
Many of the industrial biocides currently used in connection with plastics, polymers and cellulosic fibers are organometallics. These compounds are effective in preventing microbial attack on such materials. However, such compounds may be suspect for reasons of toxicity or environmental effect and problems caused by their handling and are now less accepted in some of the industrial uses in which they have hitherto been employed. It has thus become desirable to find new, non-metallic biocides for use with such materials.